With the development of the display technologies, OLED (Organic Light Emitting Diode) has been widely applied. In an OLED display panel, for each pixel, one pixel driving circuit containing OLEDs is arranged for displaying the corresponding pixel.
In known technologies, a pixel driving circuit can comprise a driving transistor, OLEDs, a storage capacitor, some transistors for controlling ON/OFF of the circuit, and so on. The driving process of the pixel driving circuit comprises two phases which are a programming phase and a light-emitting phase. In the programming phase (the first phase), a gate and a drain of the driving transistor are connected such that the driving transistor is in the saturation state, date current Idata flows through the driving transistor, and the storage capacitor records the gate-source voltage of the driving transistor under the data current. In the light-emitting phase (the second phase), the driving transistor is in the saturation state by controlling VDD and VSS. In this case, the gate-source voltage of the driving transistor is the voltage recorded by the capacitor. It can be known that the current of the driving transistor is Idata based on the relationship between the current and the gate-source voltage of the driving transistor in the saturation state. The current is also the light emitting current Ioled of the OLED.